The present invention relates initially, and thus generally, to means of forming xe2x80x9cair barriersxe2x80x9d that serve to isolate spaces without the use of a conventional physical barrier. The isolated space may be maintained at atmospheric pressure, or at greater or lesser than atmospheric pressure.
There are many possible uses of systems that utilize an air barrier to isolate one region from another. Air barriers are unique because they lack bulky physical structures that would normally be associated with any type of conventional barrier system. Air barriers find use in many different fields, including, but not limited to: air curtains, clean rooms, oxygen tents and testing chamber apparatus.
Air Curtains
An air curtain is a device specifically designed to provide a resistance to air flow through an opening, without utilizing a physical barrier. Simply put, an air curtain is a fan that is designed with an air outlet that has a low turbulent air stream (as laminar a flow as possible) that can be angled towards the incoming air stream in such a manner that the inflow of air can be prevented, and thereby creates a seal.
Air curtains can either be of the re-circulating type, or non re-circulating type. Conventional re-circulating air curtains emit air from a discharge grill on one side of the door opening and collect the air on the opposite side. It is then filtered, sometimes heated, and then is returned to the discharge grille. These units are essentially a modified heating system and use large amounts of air. They are usually associated with high initial costs and high operating costs. Also, because the air has to be filtered, the maintenance costs are also quite high. The feature is that they use low velocity air streams, which is desirable in some commercial entrances. They are usually used in supermarkets and store entrances. Thus, the need is apparent to provide an improved re-circulating air curtain.
Non re-circulating air curtains are more widely used. They are commonly characterized by lower initial and operating costs. Since non-recirculating air curtains do not re-use the air, they do not normally have to be filtered and thereby can be made essentially maintenance free.
The non-recirculating air curtain operates by discharging air at a high velocity through a narrow discharge nozzle. The discharged air stream must have the proper angle, usually 20 degrees towards the pressure side, and the air stream must be laminar for highest efficiency.
The non-recirculating air curtain operates on a very simple law of physics. One object will change its direction if it is subjected to a force, or a momentum, from another object. The momentum is found by the product of the air mass and the velocity at which it travels. The force could also be from an air mass that is increasing its velocity. The outside wind has a certain mass and a certain velocity, so does the air curtain stream. If the air curtain force (or momentum of the airflow) is equal and opposed to the force (or momentum of the airflow) from the draft through the door then the draft is prevented from entering, i.e., conservation of momentum. If the draft is much stronger than the air curtain, it will break through and some will enter. However, even in this circumstance, an air curtain will prevent some of the outside wind from entering at all times. If the air curtain is much stronger than the draft some of the air will go outside. The strength of the non-recirculating air curtain follows the formula: mass times the velocity squared. Therefore, an air curtain that blows at twice the speed has four times the wind stopping power at the same air volume.
An air curtain can be mounted above, on one side, or on both sides of a door. The most common way is to mount an air curtain above the door. Mounting the air curtain in this fashion is usually preferred because it keeps the unit out of the way and is less likely to be damaged by, for example, forklifts. It is also the most economical way of installing an air curtain. The drawback is that a small amount of air at the extreme bottom of the doorway may enter due to the height of air curtain.
An air curtain can also be mounted vertically on one side of the door. There are some disadvantages to this, however. If, for example, a truck is parked in the doorway then the entire doorway is unprotected because the truck will break the air stream. Also, with the unit mounted on one side of the door it is more likely to be damaged. Further, if there is no equal force on the other side of the door to stop the stream then the flow will follow the wall for some distance and may disturb people who are standing in the air stream.
The final way of mounting an air curtain is on both sides of the door with the air streams flowing towards each other. This is the most comfortable way of installing an air curtain as it eliminates the above drawbacks, except the possibility of damage.
In order to be able to select a proper air curtain for a given application, there are a few things that have to be considered:
(1) The physical dimensions of the opening and the space available for installation.
(2) Prevailing winds and temperatures for the opening.
(3) If there is any negative pressure in the building (this is usually caused by exhaust fans or stack effect.)
(4) The need for additional heat to be introduced in the air curtain.
(5) The need for additional heat in the areas when the door is closed and/or the need for make up air in the building.
The applications for air curtains are many. They include:
(1) Industrial Climate Control
(2) Air Conditioned Areas
(3) Industrial Oven Openings
(4) Dust and Humidity Control
(5) Mines
(6) Commercial Entrances
(7) Insect Control
(8) Cold Storage
Each of this applications will be briefly described.
Industrial Climate Control
The primary purpose of a climate control air curtain is to prevent the influx of outside air through an opening into a heated or cooled area. Openings where an air curtain would typically be used include exterior shipping and receiving doors to plants and warehouses and interior doors between plant areas of different temperatures (these applications are discussed in further detail infra). In addition, there are special applications such as the control of oven temperature, humidity and dust or the control of fresh air. Other applications include preventing the drifting of over spray from spray paint booths; blowing water off of hot steel after it has been dipped; and blowing scrap paper from a paper cutter into a collecting intake.
In order to control climate, an air curtain emits an air stream with enough velocity at a nozzle having a width commensurate with the width of the opening. For different door sizes and different wind conditions, different air velocities at the nozzle are required.
To prevent the entry of outside winds, the discharge nozzle is angled outward so that the air leaving it meets the wind trying to enter. The wind will meet or strike the air curtain stream in the doorway. When the vector representative the air stream (generated by the air curtain) and the vector representing the wind equalize, they form a resultant which should meet the floor in the door plane for maximum efficiency.
In buildings with high ceilings the air tends to stratify into a warmer layer at the ceiling and a considerably cooler one at the floor. For such buildings it is recommended that the air curtain be mounted across the top of the doorway opening and that it be provided with a top intake connected to a duct extending up to the ceiling. The warm air will then be drawn down into the air curtain and blown to the floor putting otherwise wasted heat to use. This warmer air also helps to reduce the wind chill of the moving air.
Air Conditioned Areas
Air conditioned areas are normally well balanced and seldom have negative pressure. In fact a slight over-pressure is more common where air conditioning systems are bringing fresh air into an area. Air curtains for interior doors need only be sized for the draft due to the temperature differences between the two sides. On interior openings between the air conditioned areas and non air conditioned areas, the air curtain should be mounted on the non air conditioned side. Doors between an air conditioned area and outside air are exposed to winds which must be considered in the selection of the air curtain. For application on such doors, the air curtain should be installed on the inside for the best possible efficiency, and the nozzle angle should be adjusted so that a minimum of cooled air is discharged from the inside. This inside mounting allows the air curtain to be used in the winter to prevent cold outside air from entering.
Industrial Oven Openings
It has been shown that using air curtains on openings to ovens has resulted in fuel savings of up to 40% of the total oven fuel consumption. Air Curtains are normally installed horizontally over the oven opening and angled slightly inward toward the oven to contain the hot air that is trying to come out at the top. Many air curtains are successfully operating on ovens with temperatures up to 475xc2x0 F. The air curtain drive motor should be located to the side of the oven opening to protect them from damage from hot air that would escape in the even of a shutdown of the air curtain. Oven applications should be designed case by case to meet each set of unique conditions.
Dust and Humidity Control
Air curtains should be installed on the clean or humidity controlled side of the opening, blowing toward the dirty or uncontrolled side. This will prevent the influx of the dust particles or atmospheric vapor. Common air curtain units for dust and humidity control are approximately 70% efficient. The 30% inefficiency is caused by particles of air becoming entrained in the air curtain stream and working their way through.
Mines
Air Curtains are in use in a mines, e.g., the hard rock type, at up to 1100 foot depths to control the flow of fresh air that is introduced into the mine. Installed at several points along the main airway, the air curtain deflects some of the fresh air flow out into the shafts.
Commercial Entrances
Commercial entrance air curtains are becoming widely used in building entrances to reduce energy consumption and provide comfort. In winter they retain warm inside air and prevent the influx of cold air. They can also supply additional heat in the door area using electrical, steam or hot water heaters. In the summer, air curtains keep hot humid air out and prevent the escape of cooled air. The working principle of commercial entrance air curtains is to provide the most effective air screen possible without blowing so hard that it is objectionable to people passing through.
Air curtains are ideal for application in high traffic doorways in commercial establishments such as stores, restaurants and banks. They are also ideal for public buildings such as hospitals, terminals and schools. In many cases where a vestibule was installed, or planned, to reduce the inflow, an air curtain is a better approach. This is particularly true for high traffic entrances where both doors are frequently open at the same time, defeating the purpose of the vestibule. A continuously operating air curtain allows the vestibule to be dispensed with, resulting in large savingsxe2x80x94both in initial and operating costsxe2x80x94and increasing the usable floor space.
Commercial entrance air curtains are normally mounted horizontally above a door, thereby keeping the unit out of the way and practically eliminates any chance of damage and/or accidents. During the heating season, the air stream should be directed slightly toward the outside and should never be obstructed by door operators or the door header. It is commonly recommended that the air curtain fan motor run continuously, since the power needed to operate it is minimal.
It is preferable to control the heater in heated units with a built-in or wall mounted thermostat in order to maintain a constant, comfortable temperature in the entrance area. The heater unit also provides comfort through the elimination of cold drafts and the addition of heat to door areas. Commercial entrance air curtains have many other benefits. For example, they can decrease door maintenance costs since doors need to be opened and closed less often. In restaurants they stop uncomfortable cold drafts at customers"" feet. Many schools purchase air curtains to save energy and find that, as an additional benefit, they keep floors dry and safe and hallways warm during the winter months. In buildings with high ceilings, the air curtain re-circulates the warm stratified air that rises to the ceiling.
Commercial entrance air curtains are quiet and compact and commonly pay for themselves in a very short time. Most units may be used all year round and are adjustable for seasonal conditions using either a damper or a dual speed motor.
Insect Control
Insect control air curtains, sometimes called xe2x80x9cFly Fans,xe2x80x9d are used in food processing plants, dairies, bakeries, bottling plants, restaurants, supermarkets, hospitals, school cafeterias and other areas where the control of flying insects is required. The powerful stream of air that is produced by an insect control air curtain is an excellent deterrent to insects which will usually avoid the air stream simply because of it""s unnaturally high velocity.
The most commonly effective air curtain design for insect control has a nozzle that can angle the air stream away from the area to be protected. An angle of about 20xc2x0 from the vertical is usually optimal. The unit should meet or exceed Department of Agriculture and Federal Drug Administration standards, which call for an air stream 2-inches wide at the nozzle capable of producing a minimum velocity of 1600 fpm of air 3 feet above the floor and across the entire door opening. It is very important that the entire doorway be covered so that there are no gaps for the insects to enter.
The insect control air curtains can be mounted on the inside or outside of the doorway. When mounted on the inside the unit can help control the building""s climate in the winter by stopping the influx of cold outside air. When the building contains odors which are attractive to flying insects it is recommended that the air curtain be mounted on the outside.
When a negative pressure exists inside the building, one of two approaches must be taken to make the air curtain fully effective in keeping the flying insects out. One alternative is to slightly alter the mounting of the unit, moving it out from the wall to relieve pressure on the air curtain and to allow the outside air to enter the building. The outside air will be drawn to the intake of the curtain through the gap between the wall and the unit. This gap must be covered by a screen and the gaps along the door jamb, caused by moving the unit back from the wall, should be closed by side panels.
The air curtain could be equally effective mounted horizontally or vertically. However, measures should be taken to prevent damage to the air curtain caused by traffic when mounted vertically.
Cold Storage
When opened, a door separating a cold storage area from a warm room permits a substantial loss of refrigerated air. The cold air immediately absorbs heat from the warm air. This is detrimental to the cold storage area in several ways. There are significant energy losses and safety hazards in the form of condensation and icing on the floor and fog in the doorway. Also, if enough heat is absorbed by the refrigerated area for a sufficient period of time, there may be food spoilage. Strip doors used on coolers and freezers to reduce these effects impair visibility and are unpleasant to pass through due to condensation and frosting and accumulate dirt and possible bacterial growth.
It has been proven that air curtains, when properly sized and adjusted, are up to 85% efficient in controlling the flow of air through cooler and freezer doorways. If the cold storage door is open over one hour per day, an air curtain is a cost effective way to save refrigeration costs.
Installed on the warm side of the doorway, the air curtain emits an air stream that reaches the floor at an angle and splits into two separate air streams. By properly adjusting the volume of the air and the angle of the nozzle, one air stream is made to balance against the other which is trying to leave the cooled room, while the other counteracts the warm air trying to enter. The correct air curtain sizing and adjustments must be made for each specific application so that a narrow, high velocity, low volume stream of air is projected over the entire opening creating a sufficiently stiff curtain of air. Built-in adjustments in an air curtain preferably include fully adjustable mounting brackets, variable volume controls and individually adjustable louvers in the nozzle. The narrow nozzle limits the amount of air in the doorway area and hence the turbulence, thus increasing the efficiency of the unit.
In addition to providing a substantial energy savings and increased safety, cold storage air curtains can increase the time between defrosting almost four fold, depending on the particular freezer or cooler. Also, their ability to maintain the cold room temperature right up to the doorway improves product quality and increases the useful floor space.
Clean Rooms
Clean rooms are commonly in use in manufacturing and research facilities. Simply defined, they are a dust-free working area with strict temperature and humidity control. Such control is of vital importance in the manufacture of equipment sensitive to environmental contamination, such as components for electronic and aerospace systems. Commonly, seamless plastic walls and ceilings, rounded corners, external lighting and wiring, a continuous influx of dust-free air, and daily cleaning are characteristic features. Clean room workers wear special clothing, including head coverings, and, on entering, pass through an air blast, or air shower, to remove particles. Workpieces for assembly enter through an airlock. The complicated structure of such clean rooms would benefit from a system that does not utilize physical barriers to prevent entry of particles into the isolated area.
Oxygen Tents
Oxygen tents perform two main functions: to supply oxygen-enriched breathing air (30 to 50% oxygen content) to the occupant and to cool the air within the tent by 5 to 8 degrees centigrade. It is used in the treatment of respiratory diseases and heart diseases and in certain cases for the care of persons recovering from serious operations. In cases where the patient""s breathing functions are impaired, the oxygen tent can ensure that the normal oxygen content in her or his blood is maintained, and the body temperature of a patient with very high fever can be kept down.
The oxygen tent traditionally consists mainly of a transportable cabinet (accommodating the air-circulating equipment, electric cooling unit, oxygen-dispensing unit, water atomizer, and control apparatus) and the actual tent comprising the supporting frame and the envelope, which is fitted around the patient""s bed so as to enclose it completely. A fan draws air out of the tent and passes it through a dust filter to the cooling unit. The moisture in the exhaled air is condensed and thus removed. The air is then re-circulated to the tent and is enriched with oxygen. If necessary, the atmosphere humidity can be increased by means of an artificial fog produced by the atomizer. The tent is provided with large opening, closed by zippers (zip fasteners), to give access to the patient.
However, enclosure into the solid envelope is usually uncomfortable for the conscious patient, and is unbearable by those afflicted with claustrophobia. Therefore, it is desirable to provide an oxygen tent that does not enclose a patient inside a small chamber.
Testing Chamber Apparatus
There are a variety of testing chamber apparatus used in product testing and development. Most of these apparatus focus on exposing a product or sample to a variety of environmental conditions. Commonly, the conditions are quite extreme. For example, a chamber can be made that exposes the product or sample to a certain level of humidity, temperature, or ambient pressure (to simulate the effects of varying altitude, or depth of submersion). Each of these systems require a barrier between the ambient region and the test volume. The barriers utilized in the past are almost exclusively physical in nature. The use of physical barriers means that the testing apparatus occupies a large amount of space, is heavy, bulky and expensive. One such common testing apparatus is the thermal shock chamber.
The need for true thermal shock testing has been expanding rapidly due, in part, to the enormous competitive pressures existent, particularly within the general electronics industry. The utilization of these latest technological advances for applications in medicine, computer technology, space exploration, defense research, even the automotive industry, are testimony to the increased necessity to produce products with the highest possible reliability quotient.
Thermal shock testing assists in achieving this reliability objective. Currently, more and more manufacturers are turning to full temperature cycling or thermal shock testing of their electronic components, semiconductors, computers, instruments and peripheral electronic equipment.
Thermal shock chambers allow the test specimen to be automatically and repeatedly transferred from a hot environment to a cold environment or the reverse of this temperature sequence. This process is defined as true thermal shock, as opposed to thermal cycling, wherein the specimen is introduced into the chamber and the chamber temperature is then cycled; a process which may require two hours to ramp up or down and attain, for example, a 265xc2x0 C. temperature variation.
Common thermal shock test chambers comprise two or three zones with a hot chamber, cold chamber, and/or ambient chamber. Chamber sizes are commonly available up to and beyond 27 cubic feet of interior workspace. Thus, the space, weight, and bulk of the physical chambers are significant, and it is desirable that they be reduced.
Research of the relevant prior art has found it to be devoid of references pointed to the creation of an air barrier through use of vortex forces. However, the following represent the references that the inventor believes to be the most relevant. One skilled in the art will plainly see that even these do not approach the scope of the present invention.
Berner et al U.S. Pat. No. 3,294,006 describes an apparatus for providing an enhanced efficiency air curtain used at an open doorway. Particularly, the central object of the invention is to attain with one air curtain, the efficiency commonly associated with the use of two air curtains. This is accomplished by arranging an ejection suction with the air stream from the air curtain outlet. The purpose of the suction is to suck in air or other gas and direct it, with a minimum of mixing, in the direction desired. This effect is obtained by making the nozzle length, after the ejection takes place, short enough to avoid total mixing, but long enough to get a satisfactory suction. When suction is arranged from one side only of the ejection outlet with a nozzle of proper length, all or nearly all of the sucked in air is transferred over to the opposite side of the curtain. While Berner et al does present a means for increasing the efficiency of conventional air curtains, the use of a vortex flow is neither disclosed nor contemplated.
Berlant U.S. Pat. No. 3,327,935 is directed to an air curtain having multiple blowers and changeable air inlet vanes for regulation of the air supply. The variable volumetric capacity allows adapting the air curtain to changing seasons or other changes in the output of air from the device. Also, Berlant teaches means that enhances the uniformity of output throughout the full width of the air curtain. The system of Berlant allows for adjustability to changing conditions and uniformity along its width, however, does not utilize a similar flow geometry to that described herein.
Berner et al U.S. Pat. No. 3,362,469 discloses an improved air curtain device for use between a hot and cold area. The air curtain is designed to be adjustably mounted to vary the angle with respect to the doorway in order to take controlled amounts of cold air admixed with warm air. Also, it employs a tangential impeller to help ensure a uniform, laminar flow along the width of the air curtain. Nonetheless, Berner et al does not teach the use of a vortex flow to isolate a region.
Szatmary U.S. Pat. No. 5,997,399 teaches an apparatus for providing a clean working environment. The apparatus includes an isolation booth, a worker booth, and an access device arranged to enable a worker in the worker booth to handle material in an isolation chamber formed in the isolation booth. A pressure generator is coupled with the isolation chamber to generate an air pressure that is less than the air pressure of an air curtain passing through the worker booth. This is done so that air is drawn from the air curtain in the worker booth into the isolation chamber through any air leak opening that develops in and around the access device so as to block outflow of air in the isolation chamber to the worker booth through the air leak opening. Szatmary is directed only to a chamber having an air curtain that maintains a seal between the worker and the dangerous materials such that should a leak develop in the chamber, the worker will remain safe. Szatmary does not address the use of a vortex flow to isolate the worker from the dangerous materials.
Armstrong U.S. Pat. No. 6,105,653 is directed to an air circulation barrier for use within a vehicle interior. A header is mounted within the interior of a vehicle and secured against the roof portion to extend transversely with respect to the front to back directions of the vehicle. The header supports a roller which in turn supports a flexible transparent or clear curtain which may be drawn downwardly to provide a portion of the vehicle an air barrier to divide one portion from the other. A pair of side curtains are provided along each edge of the center curtain and are extendable outwardly to provide a further barrier to air circulation or air flow past the barrier. In one embodiment, the side curtains are formed of a flexible material and are hingedly secured to the vertical edges of the center curtain. In an alternate embodiment, a pair of side rollers are pivotally secured to the header and support respective side curtains which may be extended downwardly and drawn outwardly to complete the air barrier. Armstrong teaches the use of a physical barrier to separate airspace within a vehicle in order to conserve air conditioning and heating resources. Armstrong does not teach the use of any type of fluid flow to act as a barrier.
Long et al U.S. Pat. No. 6,210,267 teaches an apparatus and method for minimizing the amount of smoke to which a shielded person is exposed. The apparatus, or air rail, has a conduit and a fan. The conduit has an air outlet through which air is forced by the fan. In operation, the fan generates an air flow that enters the conduit and exits through the air outlet. The exited air flow is directed generally away from the shielded person and is interposed between the shielded person and the smoke. The exited air flow therefore creates a barrier which minimizes the amount of smoke to which the shielded person is exposed. By minimizing the amount of smoke to which the shielded person is exposed, the apparatus and method creates a better environment for the shielded person. Long et al basically discloses a very simple air curtain that generates upward-directed streams of air to protect a person from smoke. No vortex flow is utilized or contemplated.
The present invention relates to an apparatus for isolating a volume through use of a vortex flow. The vortices are formed within ducts in an area separate from the region to be isolated, and are driven by fans. Flow straightening vanes are included to remove swirling components in the air flow. Specific applications can include oxygen tents, air curtains, testing chamber apparatus and clean rooms. While two apparatus of the present invention can be used to isolate a central volume, one apparatus can be used to isolate one volume from another.
Thus, it is an object of the present invention to provide a means for isolating a space without the use of physical barriers.
It is a further object of the present invention to utilize a vortex flow to isolate a space without the use of physical barriers.
It is an additional object of the present invention to provide means for an improved pressure chamber.
It is yet a further object of the present invention to provide means for an improved oxygen tent.
It is an additional object of the present invention to provide means for an improved air curtain.
It is yet another object of the present invention to provide means for improved testing chambers.
Another object of the present invention is to provide improved means for a clean room.